Flow measuring devices, such as, for example, vortex flow measuring devices and Coriolis flow measuring devices, include, as a rule, at least one measuring tube. Coriolis flow measuring devices can, in such case, also have two or more (for example, four) measuring tubes embodied so as to be fluidically parallel to one another. Depending on application, there is a problem, in such case, when accretion forms on the measuring tubes of the flow measuring devices (especially due to at least one part of the medium to be measured), or when abrasion (e.g. due to a corrosion) occurs on the surfaces of the respective measuring tubes contacting the medium. Especially in the case of Coriolis flow measuring devices, the oscillatory behavior of the relevant measuring tube is influenced by such accretion formation or abrasion, which in turn can lead to measurement errors in the case of measurement of a physical, measured variable (e.g. mass flow, density, viscosity, etc.). Furthermore, accretion formation as well as corrosion on measuring tubes is also problematic when a contamination of the respective medium to be measured, e.g. due to detachment of parts of the deposit, should be prevented. This is, for example, the case in food industry applications. Accordingly, it is desirable that such accretion formation and/or abrasion of a measuring tube of a flow measuring device be detectable in a reliable and simple manner, without removal of the flow measuring device or some other substantial intervention being required. In this connection, the detection of a layer-like accretion on the inner wall of a measuring tube is especially difficult to detect, since fluid can, in such case, still flow through the measuring tube in question.
In the publication WO 20091134268 A1, a flow measuring device is described, via which a deviation in a flow measuring device parameter is detectable. Such a parameter deviation can be bought about by, among other things, a plugging of a measuring tube and/or by accretion forming on a measuring tube. In the case of a described method, temperature measurements are performed at different positions of the flow measuring device, such as, for example, on the inlet side and outlet side, or alternatively, on a first measuring tube and on a second measuring tube. Therefrom, a temperature gradient is ascertained. A deviation in a flow measuring device parameter is then detected, when the ascertained temperature gradient exceeds a limit value. The method is based on the assumption that by accretion formation or plugging influences the flow through the relevant measuring tube, which, in turn, affects the temperature gradients.